This invention relates to a tracking-error correcting system for use with record medium scanning apparatus and, more particularly, to such a system wherein the support structure of a scanning transducer is deflected to change the scanning path of that transducer so as to bring the scanning path into substantial coincidence with a record track.
In signal recording and/or reproducing apparatus of the type having a rotary head assembly which scans successive parallel tracks on a record medium, signal information generally is recorded by moving the medium relative to the head assembly and by scanning the relatively moving medium. Although this general type of apparatus is useful for recording analog or digital signals representing various types of information, one particularly advantageous use thereof is to record video signal information. Accordingly, video signal recorders have been developed for use with magnetic tape, magnetic sheets, magnetic discs, and various other types of record media. While the following explanation and description is applicable to different types of recording apparatus which use different media, it is believed that such explanation and description can be significantly simplified by referring to video signal recorders which use magnetic tape, such as the video tape recorder (VTR).
In a typical VTR, one and preferably two record/playback heads are mounted on a suitable rotary assembly, and magnetic tape is helically wrapped about at least a portion of a guide drum within which are disposed the heads for scanning parallel, slant tracks across the surface of the tape. During a normal recording mode, the tape is advanced at a predetermined speed. For purposes of synchronizing the movement of the tape and the rotary movement of the heads, servo control circuitry is provided and is responsive to the vertical synchronizing signal normally provided in the video signal which is recorded. The same synchronization between the relative movement of the tape with respect to the scanning heads is achieved during a reproducing operation. Thus, the servo control circuitry is responsive to control signals which are recorded on the tape during a recording operation as well as to signals which represent the position of the rotary heads during the reproducing operation. These control and position signals serve to adjust the drive speed of the tape and, in some systems, to adjust the rotary speed of the heads. By so controlling the relative movement of the tape with respect to the heads, the heads can scan the same record tracks during a reproducing operation as were scanned during a recording operation. Therefore, during normal tape speed, synchronizing circuitry serves to insure that the scanning path of the heads substantially coincides with the previously recorded record tracks.
Desirably, many VTR systems are provided with modified reproducing operations, such as "stop," "slow-motion" and "fast-motion." In these different reproducing modes, the relative speed of movement between the tape and the scanning heads differs from the relative speed during recording. Consequently, the scanning path of the heads no longer coincides with the record track. Furthermore, the scanning path is not parallel to the record track during these different reproducing modes. Rather, the scanning path is inclined, or angularly disposed, with respect to the record track.
Heretofore, it was thought that, for accuracy in recording and reproducing video signals, the heads should be rigidly mounted to the rotary assembly. For example, if the rotary assembly is formed of rotating arms, the heads should be fixed securely to such arms. In another embodiment, if the rotary assembly is formed of one of the tape-guide drums, that is, if the guide drum assembly is formed of two face-to-face drums, one of which drums rotates, the heads should be securely mounted to the rotary drum. Although the scanning path of such rigidly mounted heads still will not coincide with the record tracks during non-normal (e.g. "stop," "slow-motion" or "fast-motion") reproducing modes, it was thought that if the scanning path could intersect the record track at the approximate mid-point of the record track, then noise or crosstalk due to the non-coincidence of the scanning path and record track could be minimized. This mid-point intersection generally can be achieved by suitably positioning, or moving the tape so as to change the exact position of the scanning path relative to the record tracks as the heads scan the tape.
It has been proposed in U.S. Pat. No. 3,787,616 that a reproducing head can be supported on a leaf assembly that is formed of piezo-electric sections which are responsive to a voltage applied thereto so as to bend or deflect, thereby deflecting the leaf assembly and moving the reproducing head. The purpose of this patent is to eliminate "jitter"; and to this effect, the leaf assembly and reproducing head are moved in a direction such that the head is displaced in the longitudinal direction of the record track, or tape. There is no recognition of correcting for a deviation between the scanning path and the skewed record track in a rotary head record/reproduce system such as a VTR.